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HASSANI S., ANTOINE L., RIDOUX V., 1997. Diets of albacore, Thunnus alalunga, and dolphins,. Delphinus delphis and Stenel la coerulaeoalba, caught in the ...

Quad. Mus. St. Nat. Livorno, 23: 79-84 (2010 )

DOI code: 10.4457/musmed.2010.23.79

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Relationships between fish size and otolith size and weight in the bathypelagic species, Beryx splendens Lowe, 1834 collected from the Arabian Sea coasts of Oman. Juma Al-Mamry1, Laith Jawad1,*, Haithem Al-Busaidi1, Saoud Al-Habsi2, Salem Al-Rasbi3

SUMMARY: The regressions between otolith size (length and width), otolith weight and fish length of the benthopelagic species, Beryx splendens living in the Arabian Sea coasts of Oman were provided. No differences between right and left otolith sizes and weight were detected by t-test, so a single linear regression was plotted against standard length (SL) for otolith length (OL), otolith width (OW) and otolith weight (OWE). Data fitted well to the regression model for both OL and OWE to SL (R2 0.6-0.8). These relationships provide a reliable tool in feeding studies and also provide support to palaeontologists in their research on fish fossils. Keywords: benthopelagic fish, otolith, otolith weight, fish-otolith sizes, Beryx, Arabian Sea, Sultanate of Oman. RIASSUNTO: In questo lavoro viene studiata la regressione tra la forma (lunghezza e larghezza), il peso degli otoliti e la lunghezza della specie bentopelagica Beryx splendens che vive nell’ambiente costiero dell’Oman nel Mare Arabico. Tramite t-test non sono state evidenziate differenze tra la forma e il peso degli otoliti destro e sinistro, è stata registrata una regressione lineare tra la lunghezza standard (SL) e lunghezza (OL), larghezza (OW) e peso (OWE) degli otoliti. I dati coincidono con il modello di regressione sia per OL sia per OWE in rapporto a SL (R2 0.6-0.8). Questo rapporto fornisce un ottimo strumento di supporto per studi sull’alimentazione e per i paleontologi nelle loro ricerche sui pesci fossili. Parole chiave: pesci bentopelagici, otoliti, peso degli otoliti, forma degli otoliti, Beryx, Mare Arabico, Sultanato dell’Oman.

Introduction Benthopelagic fishes are species usually living near-bottom environment of the deep-sea (Mauchline, Gordon, 1991) and playing an important ecological role in the transfer of energy from the top surface layer of the sea to the deep environment. During their diel vertical migration, the benthopelagic fishes feed on micronekton and return back to the deeper water layer during the daytime to avoid predation (Merrett, 1986).

The high biomass of benthopelagic fish communities in all oceans, especially in subtropical and tropical seas is an important food resource in the marine trophic web (Mauchline, Gordon, 1991, Bailey et al., 2006). Studies on feeding behaviour have shown the benthopelagic species to be among the primary trophic source for commercially important benthic fishes (Martin, Christiansen, 1997; Bergstad, Wik, 2003; McIntyre et al., 2006). Moreover, several other predators, such as marine mammals

1. Marine Science Centre, Ministry of Agriculture and Fisheries Wealth, P. O. Box 427, Postal Code 100, Muscat, Sultanate of Oman; 2. Directorate of Fisheries Research, Ministry of Agriculture and Fisheries Wealth, P. O. Box 427, Code 100, Muscat, Sultanate of Oman.; 3. Department of Marine Science and Fisheries, College of Agriculture and Marine Science, Sultan Qaboos University, Muscat, Sultanate of Oman. * Author to whom correspondence should be addressed. Tel. +96899610015; fax: +96824740159; [email protected]

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might rely on these food resources (Hassani et al., 1997; Pauly et al., 1998). The identification and quantification of the benthopelagic fish preys are frequently difficult tasks in the feeding studies (Battaglia et al., 2010). In general, the prey specimens are already partially or totally digested and the hard remains in stomachs, intestines, faeces and scats are the only diagnostic features that can be considered. Among those hard remains, otoliths are quite resistant to the digestion and they are considered the important tool for prey classification in several dietary studies (Pierce, Boyle, 1991; Pierce et al., 1991; Granadeiro, Silva, 2000). The examination of sagittae from faeces of marine mammals and sea birds usually required to examinme the regurgitated digestive pellets in order to identify the preys (Duffy, Laurenso, 1983; Johnstone et al., 1990; Pierce, Boyle, 1991). For the above reasons and for their high interspecific variability, number of keys and identification guides on fish otolith morphology has been published (Smale et al., 1995; Campana, 2004; Lombarte et al., 2006; Tuset et al., 2008). The importance of estimation of the biomass of the otolith and their numerical abundance are fundamental to understand fish prey’s energy contribution to predator diet. The relationship between fish length and otolith size and weight is usually used in several fish species to build the body size and prey biomass. In such a practice, the otolith measurement has been used (Wyllie Echeverria, 1987; Gamboa, 1991; Granaderiro, Silva, 2000; Harvey et al., 2000; Wassle et al., 2003; Lychakov et al., 2006; Battaglia et al., 2010). In paleontological studies, fossil otoliths have proved to be a good taxonomic tool to add knowledge to the taxonomic status of the ancient fauna of the planet when they compared those to the recent reference collections (Nolf 1985, 1995; Girone et al., 2006). Thus, otolith data are widely used in the fields of paleoecology, paleobathymetry, paleoclimatology, paleobiogeography and biostratigraphy (Nolf, 1995). The aim of the present study is to provide data about the relationship between otolith size (length and width) and weight and fish length of the benthopelagic teleost fish, Beryx splendens Lowe, 1834 collected from the Arabian Sea coasts of Oman. The data offer a helpful tool for feeding studies and also give support to palaeontologists in their investigation on fossils.

Materials and Methods Fish specimens were collected during the period 2007-2008 throughout the southern coasts of Oman using bottom trawls. The specimens were identified following Randall (1995). In most cases the caudal fin was damaged, so standard length (SL; most anterior point to the base of hypural plate at caudal flexion) in place of total length was considered and measured to the nearest millimetre. Sagittae were (total of 132 individuals, i.e., 264 otoliths) removed through a cut in the cranium to expose them then cleaned and stored dry in glass vials and the left and right otolith were considered separately. Specimens with obvious evidence of calcite crystallization (Strong et al., 1986) or other aberrant formations were rejected. Each sagittae, systematically placed with the sulcus acusticus oriented through the observer and its length was determined using hand-held vernier callipers and defined as the longest dimension between the rostrum and postrostrum axis (nomenclature of Smale et al., 1995) and width as the dimensions from the dorsal to ventral edge taken at right angles to the length through the focus of the otolith. Individual otolith weight (in milligram) was determined using an electronic balance. The relationship between otolith size (length, width) and weight and fish size (SL) were determined using least squares linear regression for the following parameters: otolith length (OL)fish length (SL), otolith width (OW)-fish length (SL) and otolith weight (OWE)-fish length (SL). These equations were first calculated for both left and right otoliths and the t-test was used to check any differences between regressions. The regression coefficients were compared and when significant differences (P